Geologic Wonders of the National Parks, site 25 - 30

25. White Sands National Monument, New Mexico - Contains one of the few examples of yardangs in the United States. Yardangs are streamlined, wind-eroded ridges found in arid regions. The White Sands' yardangs are well developed and impressive in size. The elongate yardangs form in the lightly cemented gypsum sand and are eroded by the prevailing southwest to northeast winds. More

26. Big Bend National Park, Texas - Contains a well preserved and clearly exposed section of rock spanning the K-T boundary. Sixty five million years ago the Cretaceous time period came to a close and the Tertiary time period began. This transition, known as the K-T boundary, is visible in the geologic record and marks one of the greatest mass extinctions of all time, and the end of the dinosaurs. Big Bend has the southernmost known exposure of terrestrial sedimentary rocks recording the K-T boundary in the United States. Big Bend is also relatively close to the Yucatan meteor impact crater believed to be responsible for the K-T mass extinction. More

27. Petrified Forest National Park, Arizona - Features one of the world's largest and most colorful collections of petrified wood. In the Triassic, trees were washed away in storms and floods and buried in an extensive floodplain under silt, mud, and volcanic ash. Ground water carrying dissolved silica from the volcanic ash crystallized around or replaced cell walls. Replacement was often so exact that even the most delicate details of the logs were preserved.
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28. Devils Postpile National Monument, California - One of the world's finest examples of columnar basalt with continuous columns over 60 ft. high. Uniform cooling conditions and homogeneity of the lava flows that filled the Middle Fork of the San Joaquin River to over 400 ft. deep helped to form the almost perfectly hexagonal columns. Around 10,000 years ago, glaciers truncated and carved into the lava flow, exposing the interior. The Devil's Postpile is one of the prominent remnants of this glaciation.
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29. Guadalupe Mountains National Park, Texas - Contains one of the Earth's finest examples of an ancient marine fossil reef. The 400 mile long Permian Capitan Reef, composed of the resistant Capitan Limestone, is well exposed in the Guadalupe Mountains. Guadalupe Mountains National Park is a must see for petroleum geologists interested in understanding reef systems. More

30. Voyageurs National Park, Minnesota - Voyageurs National Park, and Grand Teton National Park, Wyoming contain some of the oldest rocks in North America. Voyageurs, located in the southern portion of the Canadian Shield, displays rocks 2.6 - 2.85 billion years old. The oldest rocks in Grand Teton National Park are close to 2.7 billion years old and appear as complexly deformed metamorphic gneiss on Mt. Owen. The oldest rocks in America are located about 200 miles southwest of Voyagers and are up to 3.6 billion years old. More